1. Field of the Invention
The present invention relates generally to gate valve actuators and, in a particular embodiment, to apparatus and methods for a fail-safe hydraulic subsea actuator that reliably operates in deep water for extended time periods.
2. Description of the Background
Remote subsea fail-safe gate valves are typically controlled with hydraulic actuators. The hydraulic actuators and often their controls are located on the ocean floor along with other equipment. Due to the cost of positioning equipment on the ocean floor, it is desirable that any equipment be as compact as possible while still affording very high reliability. Although the location, configuration and types of actuators and controls vary, their operation is subjected to ambient sea pressure whether the actuator and controls are an open or closed system. The time required for a fail-safe valve to fail-safe close is critical, and therefore a short response time is highly desirable. The more hydraulic fluid required to operate the actuator, the longer the operation time. As water depth increases, increased hydrostatic head, or ambient sea pressure, creates forces on the valves and actuators that due to a combination of conditions can unreasonably delay or preclude fail-safe operation upon loss of hydraulic control pressure. The valve size and internal valve line pressure can create additional problems under such conditions. As well, the hydraulic fluid volume and pressure may be limited due to the need to avoid multiple hydraulic lines to the surface. Moreover, it is sometimes desirable to change out hydraulic fluid to prevent contamination that might cause actuator failure. This is another reason for limiting the amount of hydraulic fluid necessary for controlling the actuator because use of a smaller volume of fluid is quicker to exchange and/or clean. Moreover, it would be desirable to avoid hydraulic fluid contact with return springs that are used in the subsea actuators because contaminants often eventually get into the hydraulic fluid and react with the return springs thereby further increasing hydraulic fluid contamination and/or damaging the return spring.
As another matter, it would be desirable to improve indicators which can be viewed by remotely operated vehicles. In some cases, such indicators require seals that may fail and cause actuator failure. Indicators may also increase the size of the actuator.
U.S. Pat. No. 6,041,804, issued Mar. 28, 2000, to V. R. Chatufale, discloses a subsea actuator and method that includes a removable monolithic cap/hydraulic chamber that seals the actuator housing top with seals placed around the monolithic cap, defines a straight hydraulic line and port for control line hydraulic fluid, and provides for fasteners to secure the top of the subsea actuator. The monolithic cap/hydraulic chamber is so limited in metal and machine time that it can be a throw away maintenance item. A preferably cup-shaped spring pusher is provided in telescoping relationship to the hydraulic chamber. Several short hydraulic fluid passageways are provided in the bottom cup portion of the spring pusher to permit assist hydraulic control fluid into the hydraulic chamber below the piston. The driving stem provides a removable connection to the hydraulic piston from the top of the actuator housing and a quick disconnect permits disconnection of the driving stem from the valve stem. The high tension spring does not need to be removed to perform maintenance, and all wear items and seals are readily accessible. Change or replacement of the stem packing is made from the top of the bonnet to avoid dissasembling the bonnet to valve body connection. The spring chamber within the actuator housing may be increased in size to accommodate a larger spring as necessary for fail-safe operation without changing the size of the hydraulic chamber. All sliding components ride on wear rings to increase the lifetime of reliable subsea operation. The moving components are mounted in a compact, concentric configuration.
While the above actuator has many advantages, the actuator uses a significant amount of hydraulic fluid which, as explained above can sometimes be problematic. Contact of the spring with hydraulic fluid can also present a long term viability problem. It would also be desirable to limit any leakage that might occur between the valve bonnet and actuator, even if packing should leak. Moreover, the above patent does not address limiting the size of the actuator with respect to manual override operators and valve status indicators.
Furthermore, subsea actuators need to be very reliable because they operate in an environment that is not readily accessible. Conventional subsea actuators often have numerous problems that limit the operational range, reliability, cost, and maintenance thereof. While there are several commercially available subsea actuators on the market with different designs, the problems tend to be related. For instance, over long periods of time packing may leak permitting flow of fluid between the actuator housing and valve bonnet. It would be desirable to eliminate such leakage. Moreover, it would be desirable to provide that any component maintenance used to limit such leakage do not require an expensive complete exchange of the bonnet or valve stem.
In another commonly used design, the spring used for fail-safe operation is located within the hydraulic cylinder. This design is likely to cause hydraulic fluid contamination and spring damage. Moreover, while this arrangement may afford sufficient spring strength for actuation to depths of 1000 feet or so, it results in numerous problems for deep water subsea actuators. In this design, the spring outer diameter is limited to the size of the hydraulic cylinder. It is generally not desirable to increase the size of the hydraulic cylinder to provide a more powerful spring because this also increases the amount of hydraulic fluid necessary for operation and may present a potential problem at significant water depths. With a limited spring size, the fail-safe operation that the spring may afford is limited because the spring size is quite limited. Furthermore, positioning of the spring within the hydraulic cylinder also has the disadvantage of increasing the likelihood of ruining the sealing surfaces of the hydraulic cylinder due to contact with the spring during operation and also during assembly or disassembly. The damage requires replacement or reworking of the entire actuator housing and is therefore quite expensive. In this design, maintenance of even a single seal necessarily requires removal of the spring, which is normally under very high spring pressure, and may be a somewhat dangerous operation without special equipment. Typically, the entire gate valve as well as the operator must be broken down when doing virtually any maintenance. Thus, even replacing a single seal is a time consuming, costly operation. Not only is extensive time required for maintenance, but parts including additional replacement seals of all stationary metal-to-metal seals are necessary even though such may have been operating fine without problem. Thus, commonly available actuators tend to have numerous limitations including highly limited operational abilities, reliability problems, and very high maintenance costs.
Consequently, there remains a need for a compact subsea valve actuator that offers dependable operation at significant water depths, reduces the size of the manual override control, reduces the need for hydraulic fluid, reduces maintenance time, provides an improved valve/actuator status indicator system, limits leakage from the actuator to valve even if the packing should leak, permits easier maintenance, all for reduced levels of capital investment. Those skilled in the art have long sought and will appreciate the present invention which provides solutions to these and other problems.
The present invention is embodied in a design for a hydraulic subsea actuator and method for a gate valve that allows more reliable and improved operation with reduced maintenance costs for any practical water depth, e.g., 10,000 feet. The subsea valve actuator comprises elements, such as for instance, a hydraulic actuator housing, and a hydraulic piston sidably mountable within the hydraulic housing responsively to hydraulic pressure or visa-versa depending on the requirement. The hydraulic piston may be moveable to a first position for closing the valve and to a second position for opening the valve. Other elements may include, if desired, a piston indicator for indicating whether the hydraulic piston is in the first position or the second position, an override member for overriding the hydraulic pressure to control the position of the hydraulic piston manually, and an override indicator for indicating a position of the override member.
In one embodiment of the subsea valve actuator, the piston indicator and the override indicator are visual indicators although the indicators could also or alternatively be electronic, fiber optic, or other types as desired. In another embodiment, the hydraulic piston may be moveable within a hydraulic cylinder between the first position and the second position and the piston indicator may be mounted to the hydraulic actuator housing externally with respect to the hydraulic cylinder. For instance, a moveable member such as a spring pusher may be mounted within the actuator housing externally with respect to the hydraulic cylinder. The moveable member may be operably connected with the hydraulic piston and the piston indicator may be operably connected to the moveable member. The moveable member may be mounted in surrounding relationship with respect to the hydraulic cylinder. The piston indicator further comprises a shaft that engages the moveable member.
In one embodiment, an override drive shaft is moveable a first distance between an override engaged position and an override disengaged position. The override indicator may be moveable a second distance between an override engaged indication position and an override disengaged indication position. Morever, the first distance may be greater than the second distance. One preferred means for forming this embodiment may include, for instance, a first threaded portion of the override drive shaft and a second threaded portion of the override drive shaft such that the first threaded portion and the second threaded portion having different types of threads. In one embodiment, a threaded connection is found between the override drive shaft first threaded portion and the override indicator.
In another embodiment, a cylinder member defines therein the piston chamber in which the hydraulic piston may be mounted for movement. The cylinder member defines a first hydraulic fluid port into the piston chamber on a first side of the piston and a second hydraulic fluid port into the piston chamber on a second side of the piston. A plurality of seals limit movement of hydraulic fluid within the hydraulic actuator housing to the piston chamber, the first hydraulic fluid port, and the second hydraulic fluid port. A manual override assembly may be provided for manually operating the hydraulic piston. A return spring may be provided within the hydraulic actuator housing in surrounding relationship to the cylinder member such that the spring is isolated from the hydraulic fluid by the plurality of seals.
An accumulator may be connected to at least one of the first hydraulic fluid port or the second hydraulic fluid port to provide hydraulic assist to the return spring for moving the hydraulic piston to at least one of the first position or the second position.
In one presently preferred embodiment, the first hydraulic port and the second hydraulic port have an inner diameter of at least three-eighth inches to permit an increased flow of hydraulic fluid as compared to prior art devices along with a corresponding increase in actuator wall thickness.
In one embodiment, a first t-slot connection is used with the actuator shaft for interconnection with the hydraulic piston and a second t-slot connection is used with the actuator shaft for interconnection with the valve.
A packing body member may be provided in surrounding relationship to the actuator shaft or any portion of the actuator shaft assembly, a packing body seal positioned around the packing body member, a packing gland placed adjacently the packing member, and a first relief valve positioned between the packing gland and the packing body seal. A second relief valve may also be provided on an opposite side of the packing gland from the first relief valve.
In one presently preferred embodiment, a first valve member may be mounted to the actuator shaft for movement with the actuator shaft. A first seat is affixed with respect to the actuator housing in surrounding relationship to the actuator shaft. The first valve member engages the first seat for sealing around the shaft such as when the hydraulic piston is in the first position. Moreover, a second valve member may be provided in surrounding relationship to the actuator shaft with the second seat in surrounding relationship to the actuator shaft such that the second valve member seals with the second seat when the hydraulic piston is in the second position. In one embodiment, a first replaceable bushing is provided for the first seat and is used for sealing engagement with the first valve member. As well, the first valve member is replaceably mounted to the actuator shaft. For instance the first valve member may be threadably attached thereto.
In a method of the invention, steps may comprise an aspect of the invention such as for instance, providing a piston indicator for indicating a position of an actuator piston and providing an override indicator for indicating a position of a manual override assembly. The method may include providing that the piston indicator and the override indicator are detectable by a sensor of an undersea remotely operated vehicle and/or providing that the piston indicator is a shaft that does not engage the actuator piston. Moreover, the method may include providing that the override indicator has a shorter travel length than a travel length of an override member that engages the actuator piston.
The method may comprise steps such as mounting a first valve to the actuator shaft for movement therewith, providing a first seat in surrounding relationship to the actuator stem, and engaging the first valve with the first seat when the actuator shafts moves to a first position. Furthermore, the method may comprise steps such as mounting a second valve to the actuator shaft for movement therewith, providing a second seat in surrounding relationship to the actuator stem, and engaging the second valve with the second seat when the actuator shafts moves to a second position.
In one embodiment, leakage between the actuator housing and valve cavity is prevented by mounting a packing body in surrounding relationship to the actuator shaft, providing a recess in a metallic housing for receiving the packing body, mounting a packing body seal between the recess and the packing body, mounting one or more seals around the actuator shaft between the packing body seal and the gate valve for sealing leakage along the actuator shaft, and providing one or more relief valves in communication with the recess. In addition to this, leakage may be prevented by mounting a first valve member to the actuator shaft for movement with the actuator shaft and providing a seat in the packing body such that the first valve engages the seat when the actuator shaft moves to a first position.
It is an object of the present invention to provide an improved subsea hydraulic actuator and method.
It is another object of the present invention to provide a subsea actuator with a convenient configuration that can be readily modified to provide a low profile with substantial spring strength arranged so that the spring cannot damage hydraulic surfaces during manufacture, assembly, or operation.
It is yet another object of the present invention to provide a subsea hydraulic actuator with improved indicators for indicating status of the actuator and/or valve.
An advantage of the present invention is greatly reduced maintenance time and cost.
Another advantage of the present invention is the significant size (height and weight) reduction achieved by a design in accord with the invention.
Another advantage of the present invention is high performance and high reliability.
Yet another advantage of a preferred embodiment of the present invention is an absence of contact of hydraulic fluid with the return spring to avoid damage to the spring.
Yet another advantage of a preferred embodiment of the present invention is reduced contamination of the hydraulic fluid and reduced amount of hydraulic fluid required for hydraulic system cleaning purposes.
Yet another advantage of the present invention is that maintenance tends to require the exchange of less expensive components that protect elements such as the actuator/valve stem, valve bonnet and the like.
These and other objects, features, and advantages of the present invention will become apparent from the drawings, the descriptions given herein, and the appended claims.